The aim of the proposed research is to determine the mechanism by which living cells store and use energy in the form of a transmembrane electrochemical gradient for protons. The chief focus of study will be bacteriorhodopsin (bR), the bacterial light- driven proton pump. bR is currently recently the simplest, best- characterized biologically active energy transducing membrane protein and will serve as a model. The first goal is to see whether transient electrostatic changes at the membrane surface. are linked to the operation of the pump. The particular question subject to experimental test is if light-driven alterations in the distribution of surface charges assist in the transfer of the pumped protons to and from the aqueous phase. This will be probed using chemical modification of the protein, and substitution of charged and neutral lipids in native bR and-in phospholipid vesicles. Proton and nonproton ion movements will be detected using a sensitive conductivity apparatus capable of measuring absolute quantum yields and with time resolution of .001 sec. The next step will be to incorporate bR along with energy utilizing systems such as the chloroplast ATPase in reconstituted vesicles where the coupling between the two can be studied by comparison with the results with bR alone. By systematically proceeding with such reconstituted systems, the complex proton and ion movements which are presently detectable in cell envelope vesicles and whole cells can be understood. Such knowledge is critical in order to unravel the detailed molecular mechanisms of biological energy transduction.